This disclosure relates to low pressure carbon dioxide regeneration in a chilled ammonia process.
In currently existing chilled ammonia processes, carbon dioxide is extracted from flue gas and generally leaves the regenerator at pressures typically around 25 bar. Regenerating carbon dioxide at these pressures not only reduces the ammonia content of the carbon dioxide but also reduces the amount of work that is performed by compressors located downstream of the regenerator. However, the operation of the regenerator at higher pressure requires relatively high pressure (approximately 8 bar) steam, which increases the overall electrical demand on the chilled ammonia process.
Carbon dioxide is often desired by customers at pressures lower than 25 bar. At lower pressures the amount of ammonia emissions from the regenerator increases substantially and consequently this increases the stripper load with the result that the regenerator pressure is not reduced. It should be noted that for low pressure carbon dioxide regeneration, low pressure steam can be used which will save significant amounts of steam to electrical duty demand from the power plant. However, at lower pressure, the overall chilled ammonia process energy consumption increases to a point that the feasibility of operating the regenerator at lower pressure becomes un-economical (largely due to increase in stripper energy).